In recent years, flat panel displays have been used in a variety of electronic devices such as televisions, personal computers, and mobile phones. Most of the flat panel displays are liquid crystal displays (liquid crystal display devices) which utilize electric field responsiveness of a liquid crystal element.
As a typical display method of a liquid crystal display device, a twisted nematic (TN) mode is employed. However, a TN-mode liquid crystal display device, in which an electric field is applied so as to be perpendicular to a liquid crystal layer, has a disadvantage of a large change in color or luminance which depends on viewing angle, that is, narrowness of the normal viewing angle.
By contrast, a horizontal electric field mode such as an in-plane-switching (IPS) mode can be given as a display method of a liquid crystal display device which is often used besides a TN mode. In a horizontal electric field mode, liquid crystal molecules are driven by application of an electric field that is parallel to a substrate, unlike in a TN mode. Accordingly, a horizontal electric field-mode liquid crystal display device can have a wider viewing angle than a TN-mode liquid crystal display device. However, a horizontal electric field mode still has problems in contrast ratio, response time, and the like.
A ferroelectric liquid crystal (FLC) mode, an optical compensated birefringence (OCB) mode, and a mode using a liquid crystal exhibiting a blue phase can be given as liquid crystal modes in which the response time of liquid crystal molecules is shortened.
In particular, a display mode using a liquid crystal exhibiting a blue phase has a variety of advantages such as nonnecessity of an alignment film and a wide viewing angle as well as short response time. Although a liquid crystal exhibiting a blue phase has had a disadvantage of a narrow temperature range in which the blue phase is exhibited, for example, researches have been made in order to expand the temperature range by performing polymer stabilization treatment on the liquid crystal (e.g., see Patent Document 1).
In addition, in a liquid crystal display device using a liquid crystal exhibiting a blue phase, voltage higher than that for a liquid crystal used in a conventional display mode needs to be applied. Particularly in the case where a liquid crystal exhibiting a blue phase is used in a horizontal electric field-mode liquid crystal display device, an electric field needs to be horizontally applied to a liquid crystal layer and thus still higher voltage is required. As a countermeasure against this, an attempt to reduce driving voltage has been made in which a comb-like electrode is formed by forming an electrode layer so as to cover even a side surface of a convex-shaped insulating layer, whereby the area of the electrode in the substrate normal direction is increased (e.g., see Patent Document 2).